It is known that an internal combustion engine conventionally includes an engine block defining a number of cylinders. Each cylinder accommodates a piston that is coupled to a crankshaft and cooperates with a cylinder head to define a combustion chamber. A fuel and air mixture is cyclically injected into the combustion chamber and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston and thus rotation of the crankshaft.
During operation, the rotating and sliding components of the internal combustion engine are lubricated through a lubricating circuit. The lubricating circuit conventionally includes an oil sump fastened at the bottom of the engine block and an oil pump that draws motor oil from the engine sump and delivers it under pressure through a plurality of lubricating channels internally defined by the engine block and the cylinder head. An oil cooler is provided for cooling down the motor oil, once it has passed through the lubricating channels and before it returns to the oil sump. The lubricating channels usually include a main oil gallery internally defined by the engine block, whence the motor oil is directed towards a plurality of exit holes for lubricating many movable components of the internal combustion engine, before returning in the oil sump. These movable components include, but are not limited to, crankshaft bearings (main bearings and big-end bearings), camshaft bearings operating the valves, tappets and the like.
Due to this circulation, the motor oil is exposed to products of the internal combustion, such as microscopic coke particles, as well as to microscopic metallic particles produced by the rubbing of metal engine parts. Such particles may accumulate in the motor oil and grind against the part surfaces causing wear. In addition, the motor oil undergoes thermal and mechanical degradation, which progressively reduce its viscosity and reserve alkalinity. At reduced viscosity, the motor oil is not capable of lubricating the engine properly, thus increasing wear and chance of overheating. Reserve alkalinity is the ability of the motor oil to resist formation of acids. Should the reserve alkalinity decline to zero, those acids may form and corrode the engine.
For all these reasons the motor oil needs to be periodically replaced. To allow this replacement, the oil sump is usually provided with an oil drain plug that can be removed to discharge the waste oil. A standard oil drain plug is shaped as in a screw-like fashion having a cylindrical portion provided with an external thread, and a head formed at one end of the cylindrical portion for allowing the plug to be turned. This oil drain plug is screwed into a draining hole that fluidly connects the internal volume of the oil sump with the outside. In particular, the draining hole is located at the bottom of the oil sump so that, once the oil drain plug has been removed, the motor oil can flow spontaneously outside under the gravity force.
This standard oil drain plug is conventionally made of metal, because it was originally designed to be used with metallic oil sumps, for example with oil sumps made of stamped sheet metal or aluminum casting. However, some of the modern oil sumps need to be made of plastic, in order to reduce the cost and the weight of the internal combustion engines. In these cases, the screwing and unscrewing of the metallic plug during service operations could damage the thread of the draining hole. Therefore, to keep on using standard oil drain plugs, the draining hole of plastic oil sumps should be internally lined with a metallic insert. As a side effect, the metallic material of the insert would have a different thermal expansion with respect to the plastic material of the oil sump. Therefore, since the oil temperature inside the oil sump may increase up to 150° C., the different thermal expansion could cause oil leakages at the plastic/metal interface. To prevent such oil leakages, an additional gasket, typically a Press-In-Place (PIP) gasket, should to be interposed between the metallic insert an the plastic part of the oil sump.
In view of the above, it clearly turns out that the presence of a metallic insert and of a PIP gasket will complicate the manufacturing of the plastic oil sumps, thereby increasing the cost and the assembly cycle time. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.